Prepare the ox cheek by removing any sinew, pat dry and season well
Heat the oil in an ovenproof pot and brown the ox cheek, remove from the pot and set aside
Saute the onion, carrots, garlic and bay leaves in the pot for around 5 minutes on a low heat before adding the ox cheeks again
Bring up to a medium heat and add the red wine. Simmer until reduced by half before adding the flour and whisking well until the sauce starts to thicken
Add the hot beef stock, stir and bring to a simmer
Cover the pot with a lid and cook in the oven for around 4 hours until the ox cheeks are falling apart and tender. Add more beef stock if the mixture becomes dry
Near the end of the cooking time, cook the celeriac in a large pan of salted boiling water for 15 minutes or until tender
Drain, mash with butter and season to taste
Top the ox cheeks with the celeriac mash and return to the oven until the golden and crisp